Lancing devices are known in the medical health-care products industry for piercing the skin to produce blood for analysis. Typically, a drop of blood for this type of analysis is obtained by making a small incision in the fingertip, creating a small wound, which generates a small blood droplet on the surface of the skin.
Early methods of lancing included piercing or slicing the skin with a needle or razor. Current methods utilize lancing devices that contain a multitude of spring, cam and mass actuators to drive the lancet. These include cantilever springs, diaphragms, coil springs, as well as gravity plumbs used to drive the lancet. The device may be held against the skin and mechanically triggered to ballistically launch the lancet. Unfortunately, the pain associated with each lancing event using known technology discourages patients from testing. In addition to vibratory stimulation of the skin as the driver impacts the end of a launcher stop, known spring based devices have the possibility of firing lancets that harmonically oscillate against the patient tissue, causing multiple strikes due to recoil. This recoil and multiple strikes of the lancet is one major impediment to patient compliance with a structured glucose monitoring regime.
When using existing methods, blood often flows from the cut blood vessels but is then trapped below the surface of the skin, forming a hematoma. In other instances, a wound is created, but no blood flows from the wound. In either case, the lancing process cannot be combined with the sample acquisition and testing step. Spontaneous blood droplet generation with current mechanical launching system varies between launcher types but on average it is about 50% of lancet strikes, which would be spontaneous. Otherwise milking is required to yield blood. Mechanical launchers are unlikely to provide the means for integrated sample acquisition and testing if one out of every two strikes does not yield a spontaneous blood sample. It would be desirable to find improved methods to actuate the lancet.
As lancing devices have become more advanced, so have the sensors used to measure the glucose levels in the blood samples. These analyte sensors now operate using increasing lower volumes of blood sample. Some of these analyte sensors are designed for use with lancing devices that create smaller wounds, which is beneficial in that there is less pain and tissue damage, but also provide less blood to work with. As the required amount of blood decreases, it becomes increasing important to guide the ever shrinking volumes of blood towards the sensor in an efficient manner that does not waste the small volumes of blood. At low volumes, it is desirable to regulate fluid flow so that the small amounts of fluid are not wasted on surfaces that do not provide an analyte measurement.
A still further problem concerns the possible inability to guarantee blood flow from the finger lancet wound to the sensor port located on the disposable cartridge. The problem might be the invariability of the blood volume from the lancet wound, otherwise known as the shape and size of the droplet. There have been stated solutions such as the delivery of the lancet to the finger with a deeper penetration depth or a programmed controlled “lancet-in-the-finger” dwell time to sustain the size of the wound, which allows more blood to be produced from the wound. However, each might possibly result in a compromise on the degree of pain or sensation felt by the patient.
In some embodiments, a capillary may be co-located with the lancet. In order to get the blood into the capillary, several variables (lateral movement or other variation) come into play. Unless the blood droplet is directly centered on the capillary, there may be difficulty transporting enough blood to the analyte detecting member. For example, if there is any type of lateral movement or if the blood does not fall into the capillary tube, it can smear on the side wall. With an integrated sampling configuration where it may be difficult to visualize where the blood or body fluid is going, there may be no way for the subject to rectify the situation by milking the finger to get a larger droplet and increase the potential of getting the blood in.
The design of these improved medical devices has also challenged engineers to come up with more efficient methods of design. With macroscopic devices, such as conventional blood chemistry analyzers or flow cytometers, it is usually possible during the development phase to mount flow sensors, temperature probes, and optical detectors at various positions along the instrument pathway to experimentally determine the optimum operational parameters for the device. However, this approach often fails for microdevices because standard sensors and probes are typically of the same scale as the microdevice and interfere so much with device behavior that the measured data do not represent actual device performance. Thus it would be desirable to come up with design models where the most useful experimental data tend to be external measurements from which the internal physics of the microdevice should be deduced.